Comparison of the Levels of Endogenous Plant Growth Substancesin CPPlJ-treated and-untreated Kiwifruit

Seasonal changes in the endogenous levels of IAA-, GA-, cytokinin-, and ABA-like substances in the seeds and mesocarp and endocarp of CPPU [N-(2-chloro-4-pyridyl)-N'-phenylurea: (4PU-30)]-treated and-untreated kiwifruit [Actinidia deliciosa (A.Chev.) C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward] were determined.The growth of untreated fruit followed a double sigmoid curve and was divided intothree stages, but that of CPPIJ-treated fruit did not. The nucellus and endosperm in theseeds of treated and untreated fruit developed rapidly during stage I, whereas theembryo developed rapidly during stage II. Embryo development in CPPLJ-treated fruitwas slightly slower than that of untreated fruit.The levels of IAA-and GA-like substances always tended to be higher in the seedsthan they were in the flesh of treated and untreated fruit throughout the growing season.The levels of cytokinin-like substances were higher in the seeds than in the flesh duringstage I, but the reverse occured during stage II. The levels of ABA-like substances inthe seeds and flesh were nearly equal throughout the fruit growth period.Among the growth substances tested, the level of IAA-like substance in the seedscorrelated most strongly with fruit development and tended to increase toward the fruitmaturation time. The seasonal levels of GA-and cytokinin-like substances in the seedsparalleled the initial rapid developments of the fruit and seed tissues. ABA-like substance might be associated with maturation of kiwifruit because its levels in the seedsand the flesh increased toward harvest.Application of CPPU increased levels of IAA-and GA-like substances in the seedsearly in stage I and at the beginning of stage U ; it increased cytokinin-like substancesin the flesh during stage II. It is suggested that CPPU enlarges fruit not only by its highcytokinin activity but also by activating endogenous IAA, GA and cytokinin.